Filter Sock Holder Sizing: Cups, Socks, and Sump Chambers Explained

A filter sock holder is a rigid cup that sits in a sump chamber. It holds filter floss or a bag of media, in place of a cloth filter sock. Water flows through the slotted sides and drains out the bottom. It does the same job as a sock, just without the fabric.

This guide covers what a holder does differently from a cloth sock, what we build today, and a few DIY options keepers use instead.

What is a filter sock holder?

It is a rigid cup, usually slotted or perforated, that fits into a sump's back chamber. Instead of stretching a cloth sock over a rim, you set the cup in place and fill it with filter floss or a bag of media.

The flared rim rests on the chamber wall so the whole cup stays put, and the slotted body lets water pass through while it holds the media inside.

Filter sock holder vs a cloth sock: what is different?

A cloth sock is a bag. You pull it over a rim. Water runs through the fabric. When it clogs, you pull the whole thing out to rinse or replace. A holder is rigid instead. You lift it out to rinse or refill just the media inside, not a fabric bag.

Some keepers prefer a holder because there is no fabric to replace over time. Others still prefer a cloth sock for how fine its weave filters. Neither is wrong, they solve the same problem two different ways.

Does this fit my sump or reef tank?

Today we make one holder, sized for the Red Sea Max Nano's back chamber. Sump and reef tank chambers vary a lot between makers and models, so we designed this to the size we could find for that specific tank.

Chamber sizes are hand built and vary. Check the fit against your own chamber before you rely on it. More sizes may come as we hear from keepers with other tanks.

DIY filter sock holder ideas people already use

Fishkeepers have solved this without buying anything for a long time. A common fix is a plastic cup or container with holes drilled or cut in the sides, wedged or clipped into the chamber. Another is a binder clip or a zip tie holding a bag of media against the chamber wall.

None of these are sized to your exact chamber. A wedged cup can shift or tip over time, and a clip or zip tie rig can slip loose. A holder built to sit in your chamber avoids both of those problems, once the fit is right.

Frequently asked questions